1. Field of the Invention
The present invention relates to an optical material composition, and in particular, to an anti-yellowing optical material composition with high temperature resistance.
2. Description of the Related Art
The trends toward microminiaturization and price reduction of mobile phone camera modules have fostered keen interest in wafer level camera (WLC) technology. Employing wafer level manufacturing technology allows reduction of camera module size from a traditional height of 3 to 5 mm to a height of only 2 to 2.5 mm. If the material has high temperature resistance, it can also generate a 30% to 50% reduction in manufacturing costs.
In wafer level camera technology, optical components are manufactured in a wafer level. A reflowable material is used as a lens, and technologies related to semiconductor manufacturing and optical image sensor components are employed to prepare a wafer level lens. A wafer level lens module is prepared by forming thousands of lenses on a wafer using the semiconductor technology, grouping the lenses using the wafer level packaging technology, and cutting into independent lens cubes. The wafer level camera technology not only can minimize the number of required components, simplify the manufacturing process, and be applied to mass production, but can also reduce production costs.
Because the wafer level camera module is installed by using a reflow soldering method, the lens material used must have properties similar to glass materials, i.e. high temperature resistance and reflowability. At present, the plastic lenses used in mobile phone camera modules are mostly produced by using a plastic injection method and have relatively low heat resistance; such plastic lenses are not applicable to manufacturing processes for a wafer level camera module. Therefore, improved heat resistance of the lens material is an important concern for a wafer level camera module.
In addition, according to previous literature (such as TW201211078 (A)), it is known that yellowing may occur in a thermoplastic resin due to high temperature during thermoforming or after prolonged use. Because yellowing may affect availability and reliability of an optical component (such as a lens), there is a need to overcome the problem of yellowing of optical materials.
With respect to yellowing inhibition, a currently known method is adding an anti-oxidant. Such anti-oxidant includes the following two types: a free radical scavenger that traps a generated free radical and makes the free radical ineffective, and a peroxide decomposer that decomposes a generated peroxide into inert substances to inhibit generation of a new free radical. The free radical scavenger is mainly a hindered phenol compound and a hindered amine compound, and the peroxide decomposer is mainly a phosphorus compound.
However, according to TW 201211078 (A), the phosphorus compound has a low yellowing inhibition effect, and under processing conditions (such as reflow soldering) at a high temperature (such as about 260° C.), it is difficult to sufficiently inhibit yellowing. The yellowing inhibition effect is especially insufficient when the phosphorus compound is applied to an optical component (such as a lens) material, and therefore such compound is not applicable as lens material of a wafer level camera module.
According to TW 201238977 (A), if only a phenol anti-oxidant is used, the long-term anti-oxidant effect is not sufficient. Using a phenol anti-oxidant and a phosphorus anti-oxidant in combination can improve persistence of the anti-oxidant effect. However, such anti-oxidants have an insufficient anti-oxidant effect under processing conditions (such as reflow soldering) at a high temperature (such as about 260° C.). When they are applied to an optical component (such as a lens) material, the yellowing inhibition effect thereof is absolutely insufficient, and they are also not applicable as lens material of a wafer level camera module.
On the other hand, when an amount of added free radical scavenger is sufficient to inhibit yellowing, the inhibition effect of free radical polymerization generated by the free radical scavenger may adversely limit hardening of the composition, thereby reducing the toughness of a hardened product. The reason is that molecular chain scission in a polymeric material at a high temperature may generate free radicals, and these free radicals may react with other surrounding molecular chains and cause further molecular chain scission, thereby generating new free radicals. Continuous reactions result in the molecular chain of the polymeric material being shortened, mechanical performance thereof being reduced, and the material having a change of color or turning yellow.
In view of these concerns, the present invention provides an anti-yellowing optical material composition with high temperature resistance, which effectively solves the problems existing in the art.